title: Epidemiology and trends of necrotizing enterocolitis in Sweden: 1987-2009.
abstract: OBJECTIVE
  To investigate temporal, seasonal, and geographic variations in the incidence of necrotizing enterocolitis (NEC) and its relation to early infant survival in the Swedish population and in subgroups based on gestational age, birth weight, and gender.
  
  
  METHODS
  In the Swedish birth cohort of 1987 through 2009 all children with a diagnosis of NEC were identified in the National Patient Register, the Swedish Medical Birth Register, and the National Cause of Death Register. NEC incidence, early mortality, and seasonality were analyzed with descriptive statistics, Poisson regression, and auto regression.
  
  
  RESULTS
  The overall incidence of NEC was 3.4 in 10,000 live births, higher in boys than in girls (incidence rate ratio 1.22, 95% confidence interval 1.06-1.40, P = .005), with a peak in November and a trough in May, and increased with an average of ~5% a year during the study period. In most subgroups, except the most immature, an initial decrease was followed by a steady increase. Seven-day mortality decreased strongly in all subgroups over the entire study period (annual incidence rate ratio 0.96, 95% confidence interval 0.95-0.96, P < .001). This was especially marked in the most premature and low birth weight infants.
  
  
  CONCLUSIONS
  After an initial decrease, the incidence of NEC has increased in Sweden during the last decades. An association with the concurrent dramatically improved early survival seems likely.
authors.affiliation: Department of Radiology, University Hospital, 581 85 Linköping, Sweden. Margareta.Ahle@lio.se.
authors.forename: Margareta
authors.initials: M
authors.lastname: Ahle
authors.forename: Peder
authors.initials: P
authors.lastname: Drott
authors.forename: Roland E
authors.initials: RE
authors.lastname: Andersson
mesh_terms: D015331:Cohort Studies; D003430:Cross-Sectional Studies; D020345:Enterocolitis, Necrotizing / Q000453:epidemiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007235:Infant, Premature, Diseases / Q000453:epidemiology* / Q000401:mortality; D019102:Infant, Very Low Birth Weight; D008297:Male; D012621:Seasons; D012737:Sex Factors; D015996:Survival Rate; D019371:Topography, Medical
keywords: epidemiology; necrotizing enterocolitis; perinatal care; perinatal mortality; premature infants; seasonal variation; trends